Antibiotic resistance to beta-lactam antibiotics is largely due to bacterial plasmid orchromosomal beta-lactamase production. This study will define the changes in beta-lactam and cross-resistant antibiotics, beta-lactamase antivity and semi-qualitative changes in colonizing aerobic flora (stool and respiratory) induced by carbapenems and beta-lactamase inhibitor antibiotic therapy. Changes in flora will be correlated with serum and upper respiratory antibiotic concentrations.